fix(ia): dashboard newsletters settings link

[miguelpeixe]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Somewhere around changes in #3490 the settings URL got changed and the dashboard link never got updated. This PR updates the dashboard link to point to the correct page.

How to test the changes in this Pull Request:

1. While on the epic branch, confirm on Newspack -> Dashboard that clicking on the Newsletters -> Settings goes to a missing page
2. Checkout this branch and confirm that the link points to the correct page

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?